The system must prevent Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages from being accepted.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-72289	RHEL-07-040640	SV-86913r2_rule		Medium

Description
ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack.

STIG	Date
Red Hat Enterprise Linux 7 Security Technical Implementation Guide	2017-12-14

Details

Check Text ( C-72523r2_chk )
Verify the system will not accept IPv4 ICMP redirect messages. Check the value of the default "accept_redirects" variables with the following command: # /sbin/sysctl -a | grep 'net.ipv4.conf.default.accept_redirects' net.ipv4.conf.default.accept_redirects=0 If the returned line does not have a value of "0", or a line is not returned, this is a finding.

Fix Text (F-78643r2_fix)
Set the system to not accept IPv4 ICMP redirect messages by adding the following line to "/etc/sysctl.conf" (or modify the line to have the required value): net.ipv4.conf.default.accept_redirects = 0